Erosion rates on parts of the Kaikōura Peninsula more than doubled after the 2016 earthquake, showing major quakes can “rapidly alter” the way coastlines evolve, an Otago researcher says.
The Kaikōura Peninsula hosts the world’s longest-running erosion monitoring record on any rock coastline, with more than 50 years’ worth of measurements started by the late University of Canterbury Emeritus Professor Bob Kirk in 1973.
Thanks to this record, researchers from multiple institutes including the University of Otago – Ōtākou Whakaihu Waka have discovered some unexpected new findings, published in Earth Surface Processes and Landforms.
Professor Wayne Stephenson
Professor Wayne Stephenson, from Otago’s School of Geography, says the 7.8 magnitude earthquake on 14 November, 2016 lifted the Kaikōura Peninsula by about a metre, moving sections of the shore platform out of the tidal zone and creating a new marine terrace.
The latest results show erosion rates on the uplifted surfaces more than doubled after the earthquake, he says.
“This shows that major earthquakes can rapidly alter the way coastlines evolve and provides a rare example of how tectonic events reshape rock coasts.”
While the rates measured are particular to Kaikōura, the results are relevant to tectonically active coasts worldwide, particularly because more than half of the world’s shoreline is rock.
“Earthquakes regularly uplift coastlines in New Zealand, Japan, Chile, Alaska, the western United States and Mediterranean.
“We are probably the first to provide direct measurements of what happens immediately before and after an uplift event, showing dramatically altered erosion rates and processes.”
Researchers unexpectedly found that evidence of past earthquakes may disappear much more quickly than previously assumed, underscoring the importance of real-time measurement, he says.
“At Kaikōura, the uplifted coastline began eroding rapidly after the earthquake, suggesting that newly formed marine terraces may not survive long enough to preserve a complete geological record of past events.
“The evidence for the 2016 event will disappear quickly and not be preserved.”
This finding has implications for how scientists reconstruct earthquake histories, including magnitudes and frequency and assess long-term seismic hazards.
“More broadly, it improves our understanding of how earthquakes, erosion and sea-level processes interact to shape rock coasts.”
Study co-author Dr Sophie Horton, Senior Lecturer from the University of Canterbury’s School of Earth and Environment – Te Kura Aronukurangi, Te Whare Wananga o Waitaha, says the observations at Kaikōura Peninsula provide researchers with an important baseline for erosion on tectonic coastlines.
“Following the earthquake, Kaikōura Peninsula is now on a different trajectory of re-establishing an equilibrium, which may progress for some decades into the future.
“The benefit of having measurements both before and after an event like this means that we are in a much better position to fine-tune models of tectonic coastline dynamics with these observed measurements; something that has not really been achieved anywhere else in the world.”
The researchers commended the pivotal work of Emeritus Professor Bob Kirk.
“Bob’s curiosity in the 1970s about how rock coastlines operate has left an invaluable legacy on the discipline, and it’s great to see the work still being carried out at Kaikōura all these years later with new techniques and new students,” Professor Stephenson says.
